1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method which reduce the jaggy in the edge portion of an image to which halftone processing has been applied.
2. Description of the Related Art
An image forming apparatus may produce an uneven outline (jaggy) in the edge portion of a character or the like upon image processing performed during image formation. The jaggy readily occurs especially when applying halftone processing such as screen processing.
There are proposed several techniques for reducing the jaggy caused by halftone processing such as screen processing. For example, Japanese Patent Laid-Open No. 2008-199080 proposes a technique for emphasizing the outline of an object at an edge portion using image data after screen processing and that before screen processing. In this technique, it is determined whether a pixel is an edge portion of an object. If the pixel is an edge portion, it is further determined whether to output a dot in image data after screen processing. If no dot is to be output, a value derived from image data before screen processing is output. If a dot is to be output in image data after screen processing, the image data after screen processing is output.
The above-described method is effective for a multilevel printer capable of expressing a plurality of tones per pixel. However, a binary printer capable of expressing only two tones per pixel may cause an image defect. For example, in edge portion outline emphasis for an object in an intermediate color, if no dot is output in the image data after screen processing, a binary value is obtained from data before screen processing, and therefore, the maximum value is always output. For this reason, when emphasizing the outline of the edge portion, the object has a solid uniform outline with the maximum density independently of its color density, resulting in a processing result unintended by the user.
In addition, in the processing of reducing the jaggy caused by screen processing, the processing of determining whether to output a dot is complex. Hence, it may be impossible to obtain a sufficient processing speed in a low-performance environment.